In general, this invention relates to the removal of organic and inorganic contaminants from ground water. More particularly, this invention relates to a passive treatment system used with an array of non-pumping wells for such removal of contaminants.
As interest in environmental issues has increased, so has interest in improved methods of cleaning the land, air and water. In this regard, the interest in improved methods of groundwater cleanup has been acute. Potable ground water supplies worldwide are contaminated by, or threatened by, advancing plumes containing radionuclides and metals. Unlike air, land and above ground water cleanups, removal of contaminants from groundwater areas presents special problems with respect to gaining access to the contaminated areas which can make these cleanups very difficult.
Once a contaminant enters a groundwater system, it can be transported by the groundwater to a great depth. Additionally, such activities as mining or deep underground disposal of radioactive or toxic materials can create a flow of contaminants through groundwater hundreds of feet below the surface. Contamination by uranium and other radioactive materials is particularly troubling because of the longevity of these materials.
Conventional methods for treating deep groundwater contamination are largely unsatisfactory because of cost and other considerations. Active methods that seek out the underground water and bring it to the surface for treatment are most commonly used. The active methods most frequently used are so-called pump and treat methods, trenching methods, or some mixture of the two.
In a pumping method, contaminated groundwater is pumped from the contaminated lower regions to the upper regions where the-ground water may be treated and returned. The water may be brought up to the surface using drilled holes, trenches, or other means that provide access to the water for the pumping equipment. Pump and treat systems suffer from several problems. The power requirements for a pump and treat operation are very high, and can be prohibitively expensive. This is particularly true of pump systems that treat deeper ( greater than 100 feet below land surface) groundwater. Further, these systems are costly and difficult to maintain.
Trenching is even more unsatisfactory in handling deep groundwater contamination. A trenching system employs a trench dug into the ground down to the point of contamination. The exposed water is pumped from the trench or treated on site as the water flows through the trench area. Disadvantages of trenching systems include the high costs of digging the trench, and of the heavy equipment required for digging the trenches and treating the water, as well as the expense of the elaborate monitoring network that is generally used and depth limitations of the trenching equipment. Other disadvantages include the great surface disturbance associated with trenching, the cost of recontouring the surface after trenching and the increased exposure of contaminants to workers associated with this apparatus.
Because of the high costs of active systems, interest has increased in passive systems that can treat underground water without a need for actual removal of the water. The use of arrays of non-pumped wells has been proposed as a method to remediate contaminated groundwater when pump and treat or trenching technologies are not possible because of technical or financial constraints such as, for example, when contaminant streams are  greater than 200 feet below the land surface.
Prior art of interest include U.S. Pat. No. 5,512,702 (Methods for in-situ immobilization of lead in contaminated soils, wastes, and sediments using solid calcium phosphate materials); U.S. Pat. No. 5,514,279 (System for treating contaminated groundwater); and U.S. Pat. No. 5,362,394 (System for treating contaminated groundwater).
In general, prior-art methods suffer important limitations. For example, the methods include the following: the methods are effective only with respect to a small number of contaminants, the methods offer no way of treating more water than the amount in immediate contact with the treatment surface and the treatment materials are difficult to replace.
It will be evident from the foregoing, there is a need in this art of contaminated groundwater treatment for a passive, low cost system of groundwater treatment which can treat a wide variety of underground contaminants including radioactive and hydrocarbon contaminants, which can treat a large amount of water per unit, and which offers simple retrieval, replacement, and disposal of the reactive material used. In this regard, an alternative, cost effective approach to pump-and-treat methods could be of widespread applicability to the treatment of contaminated groundwater associated with abandoned and active mine sites and fractured rock systems throughout the United States and other parts of the world.
According to the invention, a groundwater decontamination system is provided for remediation of groundwater at a wide range of depths and in fractured rock systems. Among other advantages, the system includes a treatment unit which can be lowered to a desired depth so that the water at that depth will undergo decontamination. The system is relatively inexpensive, and the replacement of decontamination materials of the treatment unit can be accomplished in a simple manner.
According to one aspect of the invention, a system is provided that contains a non-pumping well decontamination unit, at least one means for lowering said unit down through said non-pumping well into an aquifer containing contaminated water and means for raising said unit out of the non-pumping well. The decontamination unit has a porous outer tube having a plurality of holes therein through which contaminated water can flow, a porous inner tube having a plurality of holes through which can flow contaminated water flowing through said outer tube, contaminant removing barrier material dispersed within the inner tube for removing on contact contaminants from the in flowing water, and a flow directing means for directing in flowing water from the holes in the outer tube to the holes in the inner tube.
Preferably, the decontamination unit has a plurality of passive samplers for monitoring contaminant removal and/or other conditions of the groundwater. The unit has fin structures for allowing the channeling of ground water into the reactive barrier material. The unit can be either permanent or replaceable, depending upon the barrier material used and concentration of the contaminant being treated.
The system can be used as part of an array of decontamination systems and an array of unpumped wells for adjusting the size of the treatment area to the size of the contamination area.
Further features and advantages of the present invention will be set forth in, or apparent from, the detailed description of a preferred thereof which follows.